Apparatus and methods for communicating using symbol-modulated subcarriers

ABSTRACT

Apparatus and methods for selecting a transmit power level and subcarrier modulation assignments based on measured channel conditions to achieve a performance level for communications over a symbol-modulated subcarrier communication channel are provided.

TECHNICAL FIELD

Embodiments of the present invention pertain to electroniccommunications, and in particular, to wireless communications, and insome embodiments, to wireless communications using symbol-modulatedsubcarriers.

BACKGROUND

Some wireless local area networks employ multi-carrier transmissiontechniques, such as orthogonal frequency division multiplexing, in whichsymbol-modulated orthogonal subcarriers are used to transmitinformation. The use of orthogonal subcarriers allow the subcarriers tobe spaced much more closely together within an available spectrum than,for example, the individual channels in a conventional frequencydivision multiplexing (FDM) system. Before transmission, the subcarriersmay be modulated with a low-rate data stream. The transmitted symbolrate of the symbols may be low, and thus the transmitted signal may behighly tolerant to multipath delay spread within the channel. For thisreason, many modem digital communication systems are usingsymbol-modulated orthogonal subcarriers as a modulation scheme to helpsignals survive in environments having multipath reflections and/orstrong interference.

Many conventional communication systems achieve higher throughput byoperating at a maximum transmit power level. These systems, however, donot consider the effects that transmit power level may have on othercommunication devices. Furthermore, these systems do not considernetwork information, the data type and the application for determiningtransmit power lever, as well as other communication parameters forcommunicating.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended claims are directed to some of the various embodiments ofthe present invention. However, the detailed description presents a morecomplete understanding of embodiments of the present invention whenconsidered in connection with the figures, wherein like referencenumbers refer to similar items throughout the figures and:

FIG. 1 illustrates a communication system in accordance with someembodiments of the present invention;

FIG. 2 is a functional block diagram of a communication station inaccordance with some embodiments of the present invention;

FIG. 3 is an information flow diagram in accordance with someembodiments of the present invention;

FIG. 4 is a flow chart of a procedure for determining communicationparameters in accordance with some embodiments of the present invention;and

FIG. 5 is a flow chart of a procedure for determining communicationparameters in accordance with some embodiments of the present invention.

DETAILED DESCRIPTION

The following description and the drawings illustrate specificembodiments of the invention sufficiently to enable those skilled in theart to practice them. Other embodiments may incorporate structural,logical, electrical, process, and other changes. Examples merely typifypossible variations. Individual components and functions are optionalunless explicitly required, and the sequence of operations may vary.Portions and features of some embodiments may be included in orsubstituted for those of others. The scope of embodiments of theinvention encompasses the full ambit of the claims and all availableequivalents of those claims.

FIG. 1 illustrates a communication system in accordance with someembodiments of the present invention. Communication system 100 mayinclude transmitting station 102 and receiving station 104, which maycommunicate over communication channel 106. Communication channel 106may comprise a plurality of orthogonal symbol modulated subcarriers.System 100 may be part of a high-throughput (HT) wireless local areanetwork (WLAN) which utilizes adaptive bit loading and transmit powercontrol for communication channels that utilize symbol modulatedsubcarriers, although the scope of the invention is not limited in thisrespect. In some embodiments, the transmit power level and subcarriermodulation assignments may be selected and updated based on measuredchannel conditions to achieve a quality of service (QOS) level for anapplication and data type. In some embodiments, the transmit power leveland subcarrier modulation assignments may be selected to achieve anacceptable packet error rate and/or an acceptable link data rate,although the scope of the invention is not limited in this respect. Insome embodiments, an acceptable packet error rate at the top of thecommunication station's physical layer (PHY) and an acceptable link datarate at the top of the communication station's MAC layer may beachieved.

In accordance with some embodiments, system 100 may use the observed ormeasured frequency selectivity and interference of channel 106 to selectsubcarrier modulation assignments for each subcarrier or groups ofsubcarriers. This may be referred to as adaptive bit loading (ABL). Thesubcarrier modulation assignment decisions may affect the overallachieved data rate depending on the modulation orders selected. System100 may also utilize transmit power control (TPC) to adjust the transmitpower. The transmit power level may be changed, for example, to reducebattery consumption and/or interference to other devices, or to supportsmall “cell” sizes. Adjustment of the transmit power level on one end ofchannel 106 may affect the ABL modulation order decisions on the otherend since each subcarrier's signal to noise ratio (SNR) may change withthe transmit power level.

In some embodiments, a communication station, such as receiving station104, may estimate channel 106 in order to select subcarrier modulationassignments via an ABL process. In these embodiments, receiving station104 may also consider asking transmitting station 102 to change itstransmit power level. In some situations, when the ABL processdetermines that low modulation levels are desired for reliablecommunications at the current transmit power level, the data rate maysuffer accordingly. Although receiving station 104 may request thattransmitting station 102 increase its power level, an increased powerlevel may create unacceptable levels of interference with othercommunication stations and increase the power consumption oftransmitting station 102. As can be seen, a tradeoff exists betweenthroughput (i.e., link data rate), link reliability, transmitter powerconsumption, and interference to other devices. In accordance with someembodiments of the present invention, communication stations 102 and/or104 may select a transmit power level and may select subcarriermodulation assignments by considering parameters not directly related tothe communication link. Examples of such parameters may include the datatype, the application and/or application requirements, networkcongestion, network aggregate throughput, and/or latency requirements.

In some embodiments, receiving station 104 may be a mobile communicationunit, while transmitting station 102 may be a more stationarycommunication unit such as an access point. In these embodiments,transmitting station 102 may be coupled with one or more externalnetworks 108 and/or the Internet 110. The terms “transmitting” and“receiving” are applied to transmitting station 102 and receivingstation 104 for ease in understanding embodiments of the presentinvention. It shall be understood that both stations may include bothtransmitting and receiving capability to establish duplex communicationstherebetween. Furthermore, although some embodiments of the presentinvention are described with respect to point-to-multipointcommunications, the scope of the present invention is equally applicableto peer-to-peer communications.

Receiving station 104 and transmitting station 102 may be almost anywireless communication device including a personal digital assistant(PDA), a laptop or portable computer with wireless communicationcapability, a web tablet, a wireless telephone, a wireless headset, apager, an instant messaging device, an MP3 player, a digital camera, anaccess point or other device that may receive and/or transmitinformation wirelessly. In some embodiments, stations 102 and 104 maytransmit and/or receive RF communications in accordance with specificcommunication standards, such as the IEEE 802.11 standards and/or theIEEE 802.16 standards for wireless local area network standards,although stations 102 and 104 may also be suitable to transmit and/orreceive communications in accordance with other techniques including theDigital Video Broadcasting Terrestrial (DVB-T) broadcasting standard,and the High performance radio Local Area Network (HiperLAN) standard.

Antennas 112 and 114 may comprise a directional or omnidirectionalantenna, including, for example, a dipole antenna, a monopole antenna, aloop antenna, a microstrip antenna or other type of antenna suitable forreception and/or transmission of RF signals. In some embodiments,antenna 112 and/or antenna 113 may be a smart antenna which may allow areduction in transmit power level to achieve a similar packet error rateor link data rate. In some embodiments, the smart antenna may alsoaffect the SNR. By changing the directivity of a smart antenna on atransmitting station, the resulting channel may look less frequencyselective to the receiver resulting in possibly a different selection ofsubcarrier modulation assignments. As a result, the ABL behavior changesin the presence of a smart antenna. In some embodiments, a smart antennamay be controlled by an algorithm that may or may not be coupled withthe communication parameter selection processes described herein. In theembodiments that include a smart antenna, the smart antenna parametersmay be set prior to channel measurements to allow subcarrier modulationassignments and transmit power level selection for a less-frequencyselective channel. In some embodiments, a smart antenna may comprise acombination of two or more antennas which result in the ability tochange the radiation pattern of a communication station to improve SNR,increase gain and/or directivity by beamforming, and/or zero forcing tohelp avoid interferers.

FIG. 2 is a functional block diagram of a communication station inaccordance with some embodiments of the present invention. Communicationstation 200 may be suitable for use as transmitting station 102 and/orreceiving station 104 (FIG. 1) although other communication devices mayalso be suitable. Communication station 200 may comprise protocol stack202, which may include one or more layers, such as application layer204, network layer 206, medium access control (MAC) layer 214, andphysical layer (PHY) 208. Layer 208 may couple with an antenna such asantenna 112 or 114 (FIG. 1). Communication station 200 may also comprisea controller to coordinate the activity of the various elements ofstation 200 and protocol stack 202.

Communication station 200 may also include application controller 210and/or network controller 212. Application controller 210 may determinethe performance level based on an application and data type. In someembodiments, network controller 212 may influence the selection of atransmit power level and subcarrier modulation assignments made byphysical layer 208 based on channel conditions to achieve a certainperformance level. In influencing the selections made by physical layer208, network controller 212 may take into account network informationdiscussed in more detail below. This is described in more detail below.

In some embodiments, physical layer 208 may be associated with areceiver and signal processing elements for receiving symbol modulatedsubcarrier communication signals and providing data signals. Physicallayer 208 may also be associated with a transmitter and signalprocessing elements for converting data signals for transmission onsymbol modulated subcarrier communication channels. For example, in someembodiments, station 200 may include an orthogonal frequency divisionmultiplex (OFDM) receiver and an OFDM transmitter associated withphysical layer 208.

In some embodiments, physical layer 208 may select subcarrier modulationrates and transmit power levels. In some embodiments, a controller, suchas network controller 212, may influence the selection of modulationrates for the subcarriers on a per subcarrier basis. Forward errorcorrection (FEC) code rates and interleaving may be adjusted to the persubcarrier modulation selections. Some examples of selecting modulationassignments for subcarriers are discussed in U.S. patent applicationSer. No. 10/122,513, entitled “WIRELESS DEVICE AND METHOD FORINTERFERENCE AND CHANNEL ADAPTATION IN AN OFDM COMMUNICATION SYSTEM”,which is assigned to the same assignee as the present application.

Although station 200 is illustrated as having several separatefunctional elements, one or more of the functional elements may becombined and may be implemented by combinations of software-configuredelements, such as processing elements including digital signalprocessors (DSPs), and/or other hardware elements. For example, thecontrollers may comprise one or more microprocessors, DSPs, applicationspecific integrated circuits (ASICs), and combinations of varioushardware and logic circuitry for performing at least the functionsdescribed herein. Although MAC layer 214 is illustrated as being next tophysical layer 208, nothing requires this. In some embodiments, MAClayer 214 may be situated above physical layer 208.

FIG. 3 is an information flow diagram in accordance with someembodiments of the present invention. Some elements illustrated indiagram 300 may be provided by a transmitting station such astransmitting station 102 (FIG. 1), and some elements may be provided bya receiving station, such as receiving station 104 (FIG. 1) althoughother communication stations may also be suitable.

In accordance with some embodiments, subcarrier modulation assignments302 may be selected based on channel conditions 304, which may bemeasured by a receiving station. Subcarrier modulation assignments 302along with transmit power level 306 may determine the possible packeterror rate and/or link data rates 308 that are achievable for aparticular channel. In some embodiments, a receiving station maydetermine the possible packet error rate and/or link data rates 308based on channel conditions 304 and transmit power level 306. In someembodiments unit considerations 312 may restrict or limit the transmitpower levels available for communications through the channel. In someembodiments, a network controller a receiving station may determinepacket error rates and/or link data rate 308, although the scope of theinvention is not limited in this respect.

Desired packet error rate and/or link data rate 314 may be determined bya receiving station. In some embodiments, desired packet error rateand/or link data rate 314 may be based on application type 316, datatype 318, quality of service level 320 and/or and network information322. An application controller of a receiving station, in conjunctionwith the application layer, may determine desired packet error rateand/or link data rate 314, although the scope of the invention is notlimited in this respect. In some embodiments, the application controllermay determine packet error rate and link data rate combinations that areacceptable to the receiving station based on data type 318, applicationconsiderations 316 and/or QOS level 320.

Application considerations 316 may include a minimum or target packeterror rate and/or minimum data rate for a particular application thatmay be operating on a communication station. Application considerations316 may also include a performance level or quality of service level forthe application. In some cases, application considerations 316 mayinclude a minimum fragment size for the application, a maximum fragmentsize, and latency considerations.

Data type 318 may include the type of data which is being communicatedor being used by an application running on a communication unit.Examples of data types include voice data, audio data, video data,gaming data, internet protocol data, file transfer data, and email data.Each data type may have a desired packet error rate and/or a data rateassociated with it, which in some cases, may depend on the applicationusing the data. Data types may also have associated latencyrequirements.

Network information 310 and 322 may include network congestion andnetwork aggregate throughput, as well as other network limitations andthroughput. Network information 310 and 322 may affect the packet errorrate and/or the link data rate. In some cases the network controller maymanage overall service to several communication stations rather thanservice to one station over an individual link. For example, the networkcontroller may wish to make sure that the several communication stationsreceive about the same link performance. Alternatively, the networkcontroller may select communication parameters so that that somecommunication stations receive a minimum bandwidth or additionalbandwidth, which may come at the expense of other stations. In thesesituations, the network controller may select an individual link to getslightly poorer throughput than it could in order to make sure that oneor more other stations get adequate service. In other situations, thenetwork controller may make individual link decisions based oninterference levels to other network cells to manage overall networkperformance rather than making individual link decisions based solely onthe individual link.

When a carrier sense multiple access with collision avoidance (CSMA/CA)channel access method is employed, there may be little or no benefit inoptimizing for a low packet error rate because a high packet error ratemay result from collisions. In this case, some embodiments of thepresent invention may optimize throughput by aiming for a higher packeterror rate with a higher raw throughput. On the other hand, when packetloss is low (e.g., either due to collision some other mechanism) andnetwork load is high, the delay for retries may be undesirable, andtherefore the network controller may emphasize a low packet error rateat the expense of raw throughput when the application traffic is knownto be delay sensitive. Where there is a low network load, the networkcontroller may recommend a reduction in transmit power to reduceinterference to neighbor networks.

Unit considerations 312 may include power level adjustment capability ofthe transmitter, the power levels available across the subcarriers, themodulation levels and modulation parameters available on a persubcarrier basis, and power consumption limitations of the transmittingstation. Channel conditions 304 may include the channel responseincluding the frequency response, frequency selectivity and/or fading ofthe channel. Channel conditions 304 may also include potentialinterference with other communications in overlapping, nearby oradjacent channels, that may result, for example, when transmit power ischanged. In some embodiments, channel conditions 304, applicationconsiderations 316, data type 318 and/or network information 322 may beknown to a receiving station, while network information 310 and/or unitconsiderations 312 may be known to a transmitting station. In theseembodiments, the combination of this information may be used by either atransmitting or receiving station to make transmit power level decisionsas well as ABL decisions.

In some embodiments, desired packet error rate and/or link data rate 314may be compared as part of element 324 with estimated packet error rateand/or link data rate 308 to determine whether the transmit power shouldbe considered to be changed. In some embodiments, the receiving stationmay notify the transmitting station of the selection of subcarriermodulation assignments, as well as the selection of transmit powerlevel. In some embodiments, the packet error rates and/or link data ratemay be varied depending on the application, data type, and/or QOS level,rather than increasing the transmit power level. In some embodiments,the transmitting station may refrain from increasing the transmit powerdepending on possible interference with other devices. Examples ofprocedures performed by transmitting and receiving stations aredescribed in more detail below.

In reference to FIGS. 1-4, some embodiments of the present inventionprovide a method for determining communication parameters. The methodmay include selecting transmit power level and subcarrier modulationassignments based on measured channel conditions to achieve aperformance level for communications over a symbol-modulated subcarriercommunication channel. The communication channel may comprise aplurality of individual orthogonal symbol-modulated subcarriers. Themodulation rates may be selected for the individual subcarriers based onthe measured channel conditions. One example of measured channelconditions may be the signal to noise and interference power ratio(SNIR) which may comprise the measured signal power divided by the sumof the received noise and the interference power.

In some embodiments, selecting the subcarrier modulation assignments mayinclude selecting no modulation, BPSK modulation, QPSK modulation, 8-PSKmodulation, 16-QAM, 32-QAM, 64-QAM, 128-QAM and/or 256-QAM for theindividual subcarriers of the communication channel. Other individualsubcarrier modulation assignments with more bits per symbol may also besuitable. In some embodiments, individual subcarriers having a betterchannel response (e.g., a higher SNR) may be assigned higher-ordermodulation assignments (e.g., having more bits per symbol) andsubcarriers having a poorer channel response (e.g., a lower SNR) may beassigned lower-order modulation assignments (e.g., having fewer bits persymbol).

In some embodiments, a desired packet error rate and/or a desired linkdata rate may be determined based on a performance level desired for anapplication and/or a data type. Whether to change the transmit powerlevel for subsequent communications over the communication channel maybe determined depending on whether the desired packet error rate and/orthe desired link data rate can be achieved based on the selectedsubcarrier modulation assignments and the selected transmit power level.

In some embodiments, an estimated packet error rate and an estimatedlink data rate may be generated for the channel based on the selectedsubcarrier modulation assignments and the transmit power level. Adecision to change the transmit power level may be based on a comparisonbetween the estimated packet error rate and/or link data rate, and thedesired packet error rate and/or the desired link data rate.

In some embodiments, the desired packet error rate and the desired linkdata rate may be based on particular data type 318. Data type 318 maycomprise voice, audio, video, gaming, internet protocol, file transferand/or email data. For example, in the case of voice data, a moderatepacket error rate and lower link data rate with a low delay limit may bedesirable. For example, in the case of audio and video data, a lowerpacket error rate and higher link data rate may be desirable, dependingon QOS level 320 which may be desired. For example, in the case ofgaming data, a lower packet error rate and higher link data rate may bedesirable. For example, in the case of internet protocol data, a lowerpacket error rate and higher link data rate may be desirable. Forexample, in the case of file transfer data and email data, a lowerpacket error rate may be desirable and a lower link data rate may beacceptable. The packet error rate and link data rate may depend on QOSlevels which may be preselected for applications and/or data types. Insome embodiments, determining a desired packet error rate and/or desiredlink data rate may be based on a desired quality of service level forthe application using data of the data type.

In embodiments, QOS parameters may comprise a combination of packeterror rate, delay limit and throughput. The packet error rate may bewithin the physical layer and may affect both link throughput (e.g.,effectively the raw throughput multiplied by one minus the packet errorrate) and the delay (e.g., the number of retries require to achievereliable transport), or the residual data unit loss rate (e.g., a packeterror rate at the top of the MAC layer). In the case of moretine-critical data, such as voice, a lower packet error rate may bedesirable to reduce retires. In the case of less time-critical data,such as internet traffic data, higher throughput at the top of the MAClayer may be more desirable, even though it may have a higher packeterror rate.

In some embodiments, a transmit power level may be decreased to lessthan a maximum power level for an application that meets a predeterminedquality of service level with a data type associated with a low datarate data or a high packet error rate. Communications may take place atthe decreased transmit power level at either a lowered link data rateselected to substantially achieve the desired packet error rate, or atan increased packet error rate selected to substantially achieve thedesired link data rate.

In some embodiments, channel conditions, such as interference that maybe caused to another communication channel, may be measured and thetransmitting station may refrain from increasing the transmit powerlevel when an increased transmit power level would cause an unacceptablelevel of interference with other communication devices. Some embodimentsmay include increasing the transmit power level to achieve a decreasedthe packet error rate or an increased the link data rate tosubstantially meet a quality of service level for the application andthe data type. Some embodiments may include refraining from increasingthe transmit power level and either communicating at a lower link datarate selected to substantially achieve the desired packet error rate, orcommunicating at a reduced packet error rate selected to substantiallyachieve the desired link data rate.

In some embodiments, the subcarrier modulation assignments for theindividual subcarriers may be selected based on a received signal, whichmay be a channel sounding preamble or some channel measurement signal.In these embodiments, data packets comprising data and training symbolsmodulated in accordance with the selected subcarrier modulationassignments may be subsequently communicated over the plurality ofsubcarriers. The data packets may be transmitted at the selectedtransmit power level.

In some embodiments, selecting the subcarrier modulation assignments andgenerating the estimated packet error rate and the estimated link datarate may be performed by a receiving station. The receiving stationand/or a transmitting station may change the transmit power level basedon the desired packet error rate and the desired link data rate.

In some embodiments, the transmitting station may refrain fromincreasing the transmit power level based network considerations,interference considerations or power consumption considerations. Thetransmitting station may reselect the subcarrier modulation assignmentsto achieve a quality of service level, and may communicate there-selected subcarrier modulation assignments to the receiving station.

In some embodiments, throughput may be optimized at a fixed orpredetermined transmit power level. In these embodiments, acommunication signal may be transmitted at a predetermined transmitpower level carrying a plurality of packets forming a burst of sizeequal to the number of packets. The signal may be received by areceiving station. For various packet error rates, the received signalmay be evaluated for various subcarrier modulation assignments andfragment sizes to determine potential link data rates. The receivingstation may select one of the potential subcarrier modulationassignments and a fragment size based on the potential link data rate toachieve the highest link data rate. The network layer packets arefragmented according to a fragment size and the fragments may beaggregated according to burst size. This allows fragments to beindividually error-checked and possibly retransmitted.

In these embodiments, a communication signal may be transmitted at thepredetermined transmit power level carrying packets at either arequested or a predetermined burst size, and the receiving station mayevaluate various subcarrier modulation assignments and fragment sizesbased on measured conditions of the communication channel. The receivingstation may further estimate a duration of a data burst and a number ofbytes expected to be received without error (e.g., the goodput) todetermine an estimated link data rate. The goodput may be defined as thePHY throughput multiplied by one minus the packet error rate. Thereceiving station may also select a combination of packet error rate andfragment size to achieve a highest link data rate. In some embodiments,the receiving station may transmit the selected subcarrier modulationassignments, the selected fragment size and an expected packet errorrate to a transmitting station, and subsequent communications may bereceived from the transmitting station in accordance with theselections.

FIG. 4 is a flow chart of a procedure for determining communicationparameters in accordance with some embodiments of the present invention.Procedure 400 may be performed by one or more communication stations,such as communication stations 102 and 104 (FIG. 1) to determinecommunication parameters for communicating over a communication linkusing symbol-modulated subcarriers. The communication parameters mayinclude the subcarrier modulation assignments for individualsubcarriers, as well as a transmit power level. In addition to channelconditions, the communication parameters may be determined byconsidering interference to other devices, network information,application requirements, data type, battery and unit levelconsiderations and/or a QOS level.

In operation 402, a receiving station may receive a communicationsignal, such as a channel-sounding preamble, from a transmittingstation. In some embodiments, the communication signal may be a requestto send (RTS) communication, although the scope of the invention is notlimited in this respect.

In some embodiments, prior to receipt of the communication signal, thereceiving and transmitting station may exchange capability information,which may be accomplished through a management frame exchange. Thisexchange may allow the receiving station to know the transmit powerlevel adjustment capability of the transmitting station, along withsubcarrier modulation assignment capability of the transmitting station.In some embodiments, the communication signal received in operation 402may be transmitted carrying a requested packet error rate and/or linkdata rate for the requested transaction. The requested packet error rateand/or link data rate may be determined by the transmitting station'snetwork controller based on information available to the transmitter,such as current data type and network information.

In operation 404, the receiving station may estimate the channel basedon the signal received in operation 402 and may select subcarriermodulation assignments based on channel measurements for the receivedpower level. In some embodiments, the receiving station may estimate thechannel based on the signal received in operation 402 and may selectsubcarrier modulation assignments to meet a packet error rate and/orlink data rate requested by the transmitter.

In operation 406, the receiving station may estimate a packet error rateand/or link data rate based on the selected subcarrier modulationassignments and the transmit power level.

In operation 408, a network controller may determine a desired packeterror rate and/or link data rate. The desired packet error rate and/orlink data rate may be determined based on application considerations,data type, and network information. In some embodiments, operation 408may be performed by a transmitting station, and prior to performingoperation 410, the receiving station may send the selected subcarriermodulation assignments and selected transmit power level selected inoperation 406 to the transmitting station.

In some embodiments, the desired packet error rate and/or link data ratemay be considered against unit considerations such as battery level, andnetwork interference considerations. In operation 410, based on theseconsideration, the network controller may reselect the transmit powerlevel and/or subcarrier modulation assignments resulting in a differentpacket error and/or link data rate.

In some embodiments in which the receiving station had requested apacket error rate and/or link data rate in operation 402, the receivingstation may send the selected subcarrier modulation assignments andselected transmit power level selected in operation 406 to thetransmitting station. In addition, the receiving station may notify thetransmitting station as to whether or not it is able to meet therequested a packet error rate and/or link data rate with the selectedsubcarrier modulation assignments. When selected subcarrier modulationassignments are not able to meet the requested a packet error rateand/or link data rate, the transmitting station may decide to increaseits transmit power level. When the selected subcarrier modulationassignments are able to meet the requested packet error rate and/or linkdata rate with sufficient margin, the transmitting station may decide toreduce its transmit power level.

In operation 412, the receiving station may be notified that thetransmitting changed the communication parameters, such as a change inthe transmit power level or a change in the subcarrier modulationassignments. Upon the completion of operation 412, the transmittingstation may communication data to the receiving station.

FIG. 5 is a flow chart of a procedure for determining communicationparameters in accordance with some embodiments of the present invention.Procedure 500 may be performed by one or more communication stations,such as communication stations 102 and 104 (FIG. 1) to determinecommunication parameters for communicating over a communication linkusing symbol-modulated subcarriers. The communication parameters mayinclude subcarrier modulation assignments for individual subcarriers, aswell as a transmit power level. Procedure 500 may be performed by acommunication station to help determine and/or optimize throughput(e.g., link data rate) at a predetermined transmit power level for agiven burst size.

In operation 502, a receiving station may receive a communicationsignal, such as a channel-sounding preamble, from a transmittingstation. In some embodiments, the communication signal may be a requestto send (RTS) communication, although the scope of the invention is notlimited in this respect. The communication signal may carry a requestedburst size and may be transmitted at a predetermined transmit powerlevel.

In operation 504, the receiving station may measure the signalproperties of the received signal, such as the signal-to-noise ratioduring the preamble. In operation 506, the receiving station mayevaluate for various packet error rates, various subcarrier modulationassignments and fragment sizes to determine potential link data rates.In operation 508, the receiving station may select one of the potentialsubcarrier modulation assignments and a fragment size based on thepotential link data rate to achieve a link data rate. In someembodiments, the receiving station may select one of the potentialsubcarrier modulation assignments and a fragment size based on thepotential link data rate to achieve the highest link data rate. In someembodiments, operation 508 may comprise estimating a duration of a databurst and a number of bytes expected to be received without error (e.g.,the goodput) to determine an estimated link data rate. In theseembodiments, the receiving station may select a combination of packeterror rate and fragment size to achieve a highest link data rate.

Operation 510 may comprise transmitting the selected subcarriermodulation assignments and the selected fragment size to a transmittingstation. In some embodiments, operation 510 may also includetransmitting an expected packet error rate to the transmitting station.Upon the completion of operation 510, the receiving station may receivesubsequent communications from the transmitting station in accordancewith the selections.

Although the individual operations of procedures 400 and 500 areillustrated and described as separate operations, one or more of theindividual operations may be performed concurrently and nothing requiresthat the operations be performed in the order illustrated.

Unless specifically stated otherwise, terms such as processing,computing, calculating, determining, displaying, or the like, may referto an action and/or process of one or more processing or computingsystems or similar devices that may manipulate and transform datarepresented as physical (e.g., electronic) quantities within aprocessing system's registers and memory into other data similarlyrepresented as physical quantities within the processing system'sregisters or memories, or other such information storage, transmissionor display devices. Furthermore, as used herein, computing deviceincludes one or more processing elements coupled with computer readablememory that may be volatile or non-volatile memory or a combinationthereof.

Embodiments of the invention may be implemented in one or a combinationof hardware, firmware and software. Embodiments of the invention mayalso be implemented as instructions stored on a machine-readable medium,which may be read and executed by at least one processor to perform theoperations described herein. A machine-readable medium may include anymechanism for storing or transmitting information in a form readable bya machine (e.g., a computer). For example, a machine-readable medium mayinclude read-only memory (ROM), random-access memory (RAM), magneticdisk storage media, optical storage media, flash-memory devices,electrical, optical, acoustical or other form of propagated signals(e.g., carrier waver, infrared signals, digital signals, etc.), andothers.

It is emphasized that the Abstract is provided to comply with 37 C.F.R.Section 1.72(b) requiring an abstract that will allow the reader toascertain the nature and gist of the technical disclosure. It issubmitted with the understanding that it will not be used to limit orinterpret the scope or meaning of the claims.

In the foregoing detailed description, various features are occasionallygrouped together in a single embodiment for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments of the subjectmatter require more features that are expressly recited in each claim.Rather, as the following claims reflect, inventive subject matter liesin less than all features of a single disclosed embodiment. Thus thefollowing claims are hereby incorporated into the detailed description,with each claim standing on its own as a separate preferred embodiment.

1. A method comprising selecting a transmit power level and subcarriermodulation assignments based on measured channel conditions to achieve aperformance level for communications over a symbol-modulated subcarriercommunication channel.
 2. The method of claim 1 further comprising:determining at least one of a desired packet error rate and a desiredlink data rate based on the performance level desired for an applicationand a data type; and determining whether to change the transmit powerlevel depending on whether the at least one of the desired packet errorrate and the desired link data rate can be achieved based on theselected subcarrier modulation assignments and the selected transmitpower level.
 3. The method of claim 2 further comprising generating atleast one of an estimated packet error rate and an estimated link datarate for the channel based on the selected subcarrier modulationassignments and the selected transmit power level, and wherein thedetermining whether to change the transmit power level is based on acomparison between the at least one of the estimated packet error rateand link data rate, and the at least one of the desired packet errorrate and the desired link data rate.
 4. The method of claim 2, whereinthe determining the at least one of the desired packet error rate andthe desired link data rate is based on whether the data type comprisesvoice, audio, video, gaming, internet protocol, file transfer or emaildata.
 5. The method of claim 4 wherein the determining the at least oneof the desired packet error rate and the desired link data rate furthercomprises determining the desired packet error rate and the desired linkdata rate based on a desired quality of service level for theapplication using data of the data type.
 6. The method of claim 2further comprising: decreasing the transmit power level to less than amaximum power level for an application that meets a predeterminedquality of service level with data having at least one of a low desireddata rate or a high permitted packet error rate; and communicating atthe decreased transmit power level at either a lowered link data rateselected to substantially achieve the desired packet error rate, or atan increased packet error rate selected to substantially achieve thedesired link data rate.
 7. The method of claim 2 further comprising:measuring channel conditions of at least one other communicationchannel; and refraining from increasing the transmit power level when anincreased transmit power level would cause an unacceptable level ofinterference with other communication devices based on the measuredchannel conditions of the at least one other communication channel. 8.The method of claim 2 further comprising increasing the transmit powerlevel to achieve at least one of a decreased the packet error rate or anincreased the link data rate to substantially meet a quality of servicelevel for the application and the data type.
 9. The method of claim 2further comprising: refraining from increasing the transmit power level;and either communicating at a lowered link data rate selected tosubstantially achieve the desired packet error rate, or communicating ata reduced packet error rate selected to substantially achieve thedesired link data rate.
 10. The method of claim 1 wherein thecommunication channel comprises a plurality of individualsymbol-modulated subcarriers, and wherein the selecting comprisesselecting modulation rates for the individual subcarriers based on themeasured channel conditions.
 11. The method of claim 10 wherein theselecting the subcarrier modulation assignments comprises selecting oneof no modulation, BPSK modulation, QPSK modulation, 8-PSK modulation,16-QAM, 32-QAM, 64-QAM, 128-QAM and 256-QAM for the individualsubcarriers of the communication channel.
 12. The method of claim 10wherein the selecting the subcarrier modulation assignments comprisesselecting the subcarrier modulation assignments for the individualsubcarriers based on a received signal, and wherein the method furthercomprises receiving data packets comprising data and training symbolsmodulated in accordance with the selected subcarrier modulationassignments over the plurality of subcarriers, the data packetstransmitted at the selected transmit power level.
 13. The method ofclaim 3 wherein the selecting the subcarrier modulation assignments andthe generating the at least one of the estimated packet error rate andthe estimated link data rate are performed by a receiving station, andwherein the method further comprises requesting, by the receivingstation, a transmitting station to change the transmit power level basedon the desired packet error rate and the desired link data rate.
 14. Themethod of claim 13 further comprising: refraining, at the transmittingstation, from increasing the transmit power level based on at least oneof either network considerations, interference considerations or powerconsumption considerations; reselecting the subcarrier modulationassignments to achieve a quality of service level; and communicating there-selected selecting subcarrier modulation assignments to the receivingstation.
 15. A method comprising: receiving a communication signaltransmitted at a predetermined transmit power level carrying packets ina burst of predetermined size; evaluating based on characteristics ofthe received communication signal for various packet error rates,various subcarrier modulation assignments and fragment sizes todetermine potential link data rates; and selecting one of the subcarriermodulation assignments and fragment sizes based on the potential linkdata rate to achieve a desired link data rate.
 16. The method of claim15 wherein: the receiving the communication signal comprises receivingthe communication signal transmitted at the predetermined transmit powerlevel carrying packets having one of either a requested or apredetermined burst size; and the evaluating comprises evaluating thevarious subcarrier modulation assignments and fragment sizes based onmeasured conditions of a communication channel through which thecommunication signal is received.
 17. The method of claim 15 wherein:the evaluating further comprises estimating a duration of a data burstand a number of bytes expected to be received without error to determinean estimated link data rate, and wherein the selecting further comprisesselecting a combination of packet error rate and fragment size toachieve a highest link data rate.
 18. The method of claim 15 furthercomprising: transmitting the selected subcarrier modulation assignments,the selected fragment size and an expected packet error rate to atransmitting station; and receiving subsequent communications from thetransmitting station in accordance with the selections.
 19. The methodof claim 15 wherein the communication signal is received through acommunication channel comprising a plurality of individualsymbol-modulated subcarriers, and wherein the selecting comprisesselecting modulation rates for the individual subcarriers based on themeasured conditions of the communication channel.
 20. The method ofclaim 19 wherein the selecting the subcarrier modulation assignmentscomprises selecting at least one of no modulation, BPSK modulation, QPSKmodulation, 8-PSK modulation, 16-QAM, 32-QAM, 64-QAM, 128-QAM and256-QAM for the individual subcarriers of the communication channel,wherein individual subcarriers having a better channel response areassigned higher-order modulation assignments having more bits persymbol, and wherein subcarriers having a worse channel response areassigned lower-order modulation assignments having less bits per symbol.21. An apparatus comprising: an application controller to determine adesired performance level for an application and data type; and aphysical layer to select a transmit power level and subcarriermodulation assignments for receipt of data over a communication channelat the desired performance level.
 22. The apparatus of claim 21 furthercomprising a network controller to determine a desired packet error rateand a link data rate based on the desired performance, wherein thenetwork controller is to further determine whether to change thetransmit power level for subsequent communications over thecommunication channel depending on whether the desired packet error rateand link data rate can be achieved based on the selected subcarriermodulation assignments and the selected transmit power level.
 23. Theapparatus of claim 22 wherein the network controller is to estimate apacket error rate and a link data rate for the channel based on theselected subcarrier modulation assignments and the selected transmitpower level, wherein network controller is to further determine whetherto change the transmit power level is based on a difference between theestimated packet error rate and link data rate, and the desired packeterror rate or desired link data rate, and wherein the network controlleris to further determine the desired packet error rate and the desiredlink data rate based on whether the data type comprises one of eithervoice, audio, video, gaming, internet protocol, file transfer or emaildata.
 24. The apparatus of claim 23 wherein the communication channelcomprises a plurality of individual symbol-modulated subcarriers, andwherein the network controller is to select modulation rates for theindividual subcarriers based on the measured channel conditions, andwherein the subcarrier modulation assignments comprise either nomodulation, BPSK modulation, QPSK modulation, 8-PSK modulation, 16-QAM,32-QAM, 64-QAM, 128-QAM and 256-QAM for the individual subcarriers ofthe communication channel.
 25. A system comprising: a omnidirectionalantenna to receive communications over a symbol-modulated subcarriercommunication channel; a physical layer coupled with the antenna toselect a transmit power level and subcarrier modulation assignmentsbased on channel conditions to achieve a performance level; and anapplication controller to determine the performance level based on anapplication and data type.
 26. The system of claim 25 further comprisinga network controller to determine at least one of a desired packet errorrate and a desired link data rate based on the performance level desiredfor the application and the data type, wherein the network controller isto further determine whether to change the transmit power level forsubsequent communications over the communication channel depending onwhether the at least one of the desired packet error rate and thedesired link data rate can be achieved based on the selected subcarriermodulation assignments and the selected transmit power level.
 27. Thesystem of claim 26 wherein: the network controller is to instruct atransmitting station to decrease the transmit power level to less than amaximum power level for an application that meets a predeterminedquality of service level with data having at least one of a low datarate data or a high packet error rate, and the transmitting station isto communicate at the decreased transmit power level at either a loweredlink data rate selected to substantially achieve the desired packeterror rate, or at an increased packet error rate selected tosubstantially achieve the desired link data rate, wherein the networkcontroller is to refrain from instructing the transmitting station toincrease the transmit power level when an increased transmit power levelwould cause an unacceptable level of interference with othercommunication devices based on measured channel conditions of the atleast one other communication channel.
 28. A machine-readable mediumthat provides instructions, which when executed by one or moreprocessors, cause said processors to perform operations comprisingselecting a transmit power level and subcarrier modulation assignmentsbased on measured channel conditions to achieve a performance level forcommunications over a symbol-modulated subcarrier communication channel.29. The machine-readable medium of claim 28 wherein the instructions,when further executed by the processors, cause the processors to performoperations further comprising: determining at least one of a desiredpacket error rate and a desired link data rate based on the performancelevel desired for an application and a data type; determining whether tochange the transmit power level depending on whether the at least one ofthe desired packet error rate and the desired link data rate can beachieved based on the selected subcarrier modulation assignments and theselected transmit power level; generating at least one of an estimatedpacket error rate and an estimated link data rate for the channel basedon the selected subcarrier modulation assignments and the selectedtransmit power level, wherein the determining whether to change thetransmit power level is based on a comparison between the at least oneof the estimated packet error rate and link data rate, and the at leastone of the desired packet error rate and the desired link data rate,wherein the determining the at least one of the desired packet errorrate and the desired link data rate is based on whether the data typecomprises voice, audio, video, gaming, internet protocol, file transferor email data, and wherein the determining the at least one of thedesired packet error rate and the desired link data rate furthercomprises determining the desired packet error rate and the desired linkdata rate based on a desired quality of service level for theapplication using data of the data type.
 30. The machine-readable mediumof claim 29 wherein the communication channel comprises a plurality ofindividual symbol-modulated subcarriers, and wherein the selectingcomprises selecting modulation rates for the individual subcarriersbased on the measured channel conditions, and wherein the selecting thesubcarrier modulation assignments comprises selecting one of nomodulation, BPSK modulation, QPSK modulation, 8-PSK modulation, 16-QAM,32-QAM, 64-QAM, 128-QAM and 256-QAM for the individual subcarriers ofthe communication channel.